Appearing Tuesday on Fox News Channel's "On the Record with Greta Van Susteren," Williams said he wants to see Hekmati and other Americans held in Iran released as the United States wraps up nuclear talks with Iran.

"This man is being held illegally," he told Van Susteren. "I do know for a fact after reaching out and talking to members of Amir's family that our State Department is not talking to them. We don't know what's going on."

Iran allowed Hekmati to come in the country "just so they could do this to him," Williams said. "This is a Marine who fought against Iraq. They know that is his history."

Williams said he believes Hekmati is being held as a bargaining chip in the nuclear negotiations.

"For three and a half years, this man has been tortured," Williams said. "He has been put in three-by three-cells. He has been whipped on his feet. He has been addicted to drugs so that they can torture him through his withdrawal."

Hekmati's parents left Iran in 1979 when the country was in turmoil, but he is a U.S. citizen, born in Arizona and raised in Michigan. He fought in the Iraq War, and when he traveled to Iran to visit his dying grandmother in 2011 was charged by Iran with spying for the United States.

He originally was sentenced to death, but after a retrial a year ago, was sentenced to 10 years in prison. He as dual American and Iranian citizenship, but renounced his Iranian citizenship in hopes of receiving help from another country, Williams said.

"Look, I don't expect him to call me, but I expect him to tell our country that we do what we promised we leave no soldier behind," Williams said. "Find out how many people are going to sign up the next time we want to go to war when we keep doing this to those who have fought to protect us."